This invention relates generally to electrical connector and cable assemblies and, more particularly, to an assembly of a multi-pair cable terminated by a modular plug for use in the transmission of high frequency signals.
Data communication networks are being developed which enable the flow of information to ever greater numbers of users at ever higher transmission rates. A problem is created, however, when data is transmitted at high rates over a plurality of circuits of the type that comprise multi-pair data communication cable. In particular, at high transmission rates, each wiring circuit itself both transmits and receives electromagnetic radiation so that the signals flowing through one circuit or wire pair (the "source circuit") may couple with the signals flowing through another wire pair (the "victim circuit"). The unintended electromagnetic coupling of signals between different pairs of conductors of different electrical circuits is called crosstalk and is a source of interference that often adversely affects the processing of these signals. The problem of crosstalk in information networks increases as the frequency of the transmitted signals increases.
In the case of local area network (LAN) systems employing electrically distinct twisted wire pairs, crosstalk occurs when signal energy inadvertently "crosses" from one signal pair to another. The point at which the signal crosses or couples from one set of wires to another may be 1) within the connector or internal circuitry of the transmitting station, referred to as "near-end crosstalk", 2) within the connector or internal circuitry of the receiving station, referred to as "far-end crosstalk", or 3) within the interconnecting cable.
Near-end crosstalk ("NEXT") is especially troublesome in the case of telecommunication connectors of the type specified in sub-part F of FCC part 68.500, commonly referred to as modular connectors. Such modular connectors include modular plugs and modular jacks. The EIA/TIA (Electronic/Telecommunication Industry Association) of ANSI has promulgated electrical specifications for near-end crosstalk isolation in network connectors to ensure that the connectors themselves do not compromise the overall performance of the unshielded twisted pair interconnect hardware typically used in LAN systems. The EIA/TIA Category 5 electrical specifications specify the minimum near-end crosstalk isolation for connectors used in 100 ohm unshielded twisted pair Ethernet type interconnects at speeds of up to 100 MHz.
A high speed data transmission cable is typically terminated by a modular plug which conventionally comprises an insulating housing in which a planar array of closely spaced parallel passages receive the ends of respective cable wires. The cable typically comprises four circuits defined by eight wires arranged in four twisted pairs and is typically terminated by modular plug having eight contacts engaging the ends of the eight wires, which are received in respective wire-receiving passages arranged in a row. Specified ones of the four pairs of the plug contacts are assigned to terminate respective specified ones of the four cable wire pairs according to ANSI/EIA/TIA standard 568. For example, the standard 568 contact assignment for the wire pair designated #1 are the pair of plug contacts located at the 4-5 contact positions. The cable wires of the pair designated #3 are, according to standard 568, terminated by the plug contacts located at the 3-6 positions which saddle the 4-5 plug contacts that terminate wire pair #1. Near-end crosstalk between wire pairs #1 and #3 during high speed data transmission has been found to be particularly troublesome in modular plugs that terminate cable according to standard 568.